1969 Firebirds had F70/14 from the factory. F7014 is 25.6" tall 225/70/14 is 26.4"
We run 245/60/14 on the rear (25.6"), and 225/60/14 on the front. We have run up to 230/60/14 on the front, but the nose was a little too high.
The F70s Coker sells in a bias ply are 26.2". They also sell a radial version in that size that are 26.4", but I'm guessing it's really just a renamed 225/70.